Quick, Before It Molts

By ANDY NEWMAN

Published: August 8, 2006

David L. Wagner was beating the bushes in a state park here the other day, hoping to flush out new kinds of caterpillars, when a colleague walked over and presented for inspection a plump, milky-green creature he had just found crawling on a leaf. The caterpillar was not particularly rare, but Dr. Wagner set down his stick to greet an old friend.

''Abbot's sphinx!'' he called out. ''One of our only talking insects.''

He trained his ever-present field magnifier on the bug's back, which sprouted a cadmium-yellow horn-shaped protuberance. After the next molt, Dr. Wagner said, ''the horn turns into an eyelike button -- it actually looks like your eye -- and if you touch the eye the caterpillar reels around and squeaks like a mouse. Scares the bejesus out of you, is what it does.''

Dr. Wagner went back to whacking at grass stalks with renewed vigor. ''You don't need to go to the Amazon,'' he said. ''You don't need to go to New Guinea. You go out your back door with a hand lens and you'll find some pretty amazing things that a lot of people have overlooked.''

More than 600 of those things populate the pages of ''Caterpillars of Eastern North America'' (Princeton University Press, 2005), a lusciously photographed book generally regarded as the most comprehensive field guide ever to caterpillars, as opposed to their better-documented adult forms -- moths and butterflies.

In the book, the fruit of a decade's research, Dr. Wagner, an associate professor of ecology at the University of Connecticut, argues passionately that creeping things can be every bit as mesmerizing and transporting as those that flit and dart in the air.

Take, for instance, the camouflaged looper, an inchworm that cloaks itself in shredded bits of the flower it is feeding on. ''A Mardi Gras caterpillar that is out of costume only after a molt,'' Dr. Wagner writes. Or the orange dog, scion of the handsome but rather mundane-looking giant swallowtail butterfly. The orange dog looks like a squirt of fresh bird droppings with two long retractable magenta fangs; as the book notes approvingly, ''a caterpillar with excellent options in both bird-dropping and snake-mimicry.''

Though Dr. Wagner has observed more than 1,000 species in his backyard in Storrs, in northeastern Connecticut, he found much to interest him here at Hurd State Park, less than 30 miles south.

At the edge of a grassland by the Connecticut River, he examined his beating sheet, a white nylon kite stretched across a wood frame, and picked up a beige, wormy-looking caterpillar with dark brown streaks running along its back. ''I don't think I've seen that one before,'' he said.

In just the past year, Dr. Wagner has discovered and described a half-dozen species that had either never been observed in their caterpillar state or were new to science altogether -- a fact that says much about the primitive state of caterpillar studies.

''Caterpillars are the last unknown group of big things on the terrestrial world,'' said Daniel H. Janzen, an ecologist at the University of Pennsylvania who has studied the caterpillars of one corner of Costa Rica for 25 years.

''You step off a plane in some place like Venezuela and walk out into the forest, pick up a fruit or a skull or a butterfly or a bird -- anything big enough to hold in your hand -- it's got a name, and there is someone who can tell you what it is,'' he said. ''That's not true for caterpillars, the world around.''

There are several reasons. Few reference-quality collections of specimens exist, because, unlike birds and beetles and butterflies, dead caterpillars do not keep well. Scientists have tried pickling them in alcohol, or hollowing them out and blowing them up like little balloons, but both techniques distort them badly.

And until recent advances in DNA science, the only way to identify a caterpillar positively was to rear it to adulthood, which requires careful husbandry. (There are well-known moths whose caterpillars have never been seen by science.) Most caterpillars shed their skins five or six times as they grow, and each stage, or instar, can have radically different markings and patterns from the previous one.

''In order to do this well, you sort of had to know the entire universe,'' said Dr. Wagner, who said that 5 percent to 10 percent of the caterpillars in his book had never before been studied through their entire life cycles. The 700 species in the book are only a small fraction of the 5,000 east of the Mississippi.

Dr. Wagner, a tall 49-year-old Californian whose trim mustache and lantern jaw lend him an air of the safari, started out as a botanist but was drawn to insects and then caterpillars by luck and circumstance.

In 1992, for research on how a common bio-organic pesticide used against gypsy moth caterpillars affected other species, he and his team collected 12,000 caterpillars in a Virginia forest and reared them to adulthood. The data yielded a guide to 50 common forest caterpillars. The federal Forest Service printed 5,000 copies, which were snapped up in a few months.